<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta name="viewport" content="width=device-width,user-scalable=no,initial-scale=1.0,maximum-scale=1.0,minimum-scale=1.0">
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<title>无标题文档</title>

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<style type="text/css">
*{margin:0;padding:0;}
           .layer1{width:100%; height:200px;background:#FC3;}
		           .layer1-1{width:100%;height:150px;background:#F93;text-align:center;font-size:36px;}
				   .layer1-2{width:100%;height:50px;background:#666;}
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		           .layer2-1{width:50%;height:300px;background:#963;float:left;}
				   .layer2-2{width:50%;height:300px;background:#C36;float:left;}
				   .layer2-3{clear:both;}
           .layer3{width:100%; height:150px;background:#306;}     
		           @media screen and (min-width: 900px) and (max-width: 1200px)
				   {  
					 .layer2-1{width:50%;}
					 .layer2-2{width:50%;} }
				   @media screen and (max-width: 900px)
				   {  
					 .layer2-1{width:100%;}
					 .layer2-2{width:100%;} }
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<body>
       <div class="layer1">
            <div class=layer1-1></div>
            <div class=layer1-2></div>
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       <div class="layer2">
            <div class=layer2-1></div>
            <div class=layer2-2></div>
            <div class=layer2-3></div>
       </div>    
       <div class="layer3"></div>

</body>
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